Chemicals such as ozone and chlorine are used to perform sterilization and disinfection of city water and underground water, sterilization, disinfection, and decoloration of industrial water, or bleaching of pulp, and further sterilization of medical equipment and the like.
In a conventional disinfection device, since a retention vessel and a stirring device such as a spray pump are necessary to uniformly dissolve ozone and a chemical in water to be processed, a change of water quality and water amount cannot be instantly coped with. In contrast, since ultraviolet rays have sterilizing, disinfecting and decoloring actions, deodorizing and decoloring actions of industrial water, or a bleaching action of pulp, and the like, the ultraviolet rays have a merit of instantly coping with a change of water quality and water amount. Thus, recently, an attention has been paid to an ultraviolet irradiation device that sterilizes and purifies water by irradiating water to be processed with ultraviolet rays as one of sterilization-disinfection means. Jpn. Pat. Appln. KOKAI Publication No. 2004-223502 discloses an ultraviolet sterilization-purification device having a function of detecting a crack and damage of a protection pipe for protecting an ultraviolet lamp, and the like.
However, the ultraviolet sterilization-purification device has the following problems.
(1) When ultraviolet rays are used, supplied water and sewage water are sterilized, disinfected, and inactivated within a few seconds during which they are irradiated with ultraviolet rays from an ultraviolet source. However, when an ultraviolet lamp with a high brightness and a high output is used as an ultraviolet source, since the lamp has a short life, a predetermined ultraviolet output, which is necessary for disinfection, sterilization, and inactivation, cannot be ensured until a periodic maintenance cycle per year is reached.
(2) When the ultraviolet lamp is used as the ultraviolet source, the predetermined ultraviolet output, which is necessary for disinfection, sterilization and inactivation, cannot be ensured until a lamp life is reached depending on operation history such as the number of turnon and turnoff times, an environment in which the ultraviolet lamp is installed, and an increase and decrease of a lamp input.